The invention relates to a process and an apparatus for carrying out the process for continuous preparation of polyamides, the monomeric starting material for which is composed of up to 100% of adipic acid/hexamethylenediamine salt and water.
For polymerizing adipic acid/hexamethylenediamine salt (AH salt) or adipic acid and hexamethylenediamine, it is known that an aqueous AH salt solution can be used as starting material and be heated in a pressurized reactor to a temperature in the range of 220 to 280.degree. C. in order to prepare an AH precondensate in which the NH.sub.2 groups of the hexamethylenediamine have reacted with the COOH groups of the adipic acid.
It is known that the aqueous adipic/hexamethylenediamine solution is heated under a pressure which is lower than the vapor pressure of the solution, with simultaneous evaporation of the water, and that the most volatile material driven off, hexamethylenediamine, is collected in a column and reintroduced to the polymerization process (U.S. Pat. No. 2,689,839; U.S. Pat. No. 3,960,820). When the pressure acting on a precondensate of this type is released, small amounts of hexamethylenediamine can escape. To compensate for the excess of acid, which reduces viscosity, an excess of hexamethylenediamine is added (U.S. Pat. No. 3,193,535; DE 2,417,003). Using known processes, water is removed from the polyamide melt, and the melt is post-condensed.